1. Technical Field
The invention relates to the field of the stabilization and absorption of lipids containing long-chain polyunsaturated fatty acids.
2. Background Art
Two long-chain polyunsaturated fatty acids (LC-PUFA), docosahexaenoic acid (DHA, C22:6, n-3) and arachidonic acid (AA, C20:4, n-6) are major LC-PUFAs in human milk fat. DHA is essential for the development of the brain and of sight and AA is associated with the immune function and with the growth of young children. That is why sources of these acids are added to infant products, in general in the form of mixtures of triacylglycerols (TAGs) enriched with the LC-PUFAs in question. These may be mixtures of concentrates of AA and DHA of fermentation origin or alternatively of a concentrate of AA of fermentation origin supplemented with fish oil predominantly containing DHA and, in a smaller quantity, eicosapentaenoic acid (EPA, C20:5 n-3).
LC-PUFAs are extremely sensitive to oxidation. Their oxidative degradation and the deterioration of the associated quality manifests itself by unpleasant odors and a reduction in the nutritional quality of the mixtures of TAGs.
It is described in U.S. Pat. No. 5,686,131 that the oxidative stability of the LC-PUFAs can be improved by the interesterification of an oil which is very rich in PUFA having a degree of unsaturation of at least 3 and of an oil containing long-chain saturated fatty acids, of C16 to C22 (LC-SFA). The product obtained has a high melting point, up to 80xc2x0 C. due to the presence of a certain quantity of trisaturated TAGs, which makes it difficult to handle in a food production because of the high risk of oxidative deterioration during its melting which requires prolonged heating at high temperature. Furthermore, the TAGs containing only long-chain saturated fatty acids are absorbed more slowly than those which contain medium-chain saturated fatty acids (MC-SFAs). The LC-SFAs are only very slightly absorbed when they are at positions 1 and 3 of the TAGs. Because they form insoluble salts with calcium, these non-absorbed LC-SFAs induce a reduction in the absorption of calcium. Finally, the product of the inter-esterification is deodorized at high temperature, greater than 240xc2x0 C., which is likely to generate trans fatty acids which are not recommended in dietetic applications.
Thus there is a need for improved compositions of such fatty acids.
The invention relates to a stabilized lipid composition of randomly interesterified triacylglycerols comprising, by weight of fatty acid components long-chain polyunsaturated fatty acids having at least 20 carbon atoms and a degree of unsaturation of at least 4 and being present in a nutritionally beneficial amount but less than 5% by weight; and medium-chain saturated fatty acids having six to fourteen carbon atoms and being present to promote absorption of the LC-PUFAs. Preferably, the TAGs containing LC-PUFAs almost exclusively are mono-LC-PUFA.
The LC-PUFAs predominantly comprise arachidonic acid, docosohexaenoic acid, eicosopentaenoic acid or mixtures thereof, with the AA and DHA being predominantly in the LC-PUFAs of the TAGs.
The MC-SFAs generally comprise coconut, basbassu or palm kernel fats or natural or synthetic medium chain triglycerides containing caproic acid, caprylic acid, capric acid, lauric acid, myristic acid or mixtures thereof. Thus, the MC-SFAs can have eight to ten carbon atoms, or ten to twelve carbon atoms.
The invention also relates to a nutritional product that contains lipids, wherein at least a portion of the lipids include the lipid composition of the invention. The lipids are present in the product in an amount of 15 to 35% by weight of dry matter, with the lipid composition of the invention preferably representing 5 to 50% of that amount.
The invention also relates to an infant food, which further comprises the nutritional product of the invention and one or more components of proteins, hydrolysed proteins, carbohydrates, vitamins and trace elements. This food may be in the form or a liquid or in dry form.
The invention also relates to a process for the preparation of lipid compositions of the invention. This process includes the steps of interesterifying a mixture of (A) 1 to 20% of an oil that is rich in LC-PUFAs having a degree of unsaturation of at least 4 and (B) 80 to 99% of an oil that is rich in MC-SFAs at a sufficient temperature ad for a sufficient time in the presence of a catalyst to form a product where fatty acids are randomly distributed on a glyceryl backbone; washing the product to remove alkaline and soap residues; refining the product by removing secondary products of the interesterification and traces of soap from the washed product; and deodorizing the refined product to obtain a deodorized, decolorized, stabilized lipid composition. Additional features of the process are described hereinbelow.
The aim of the invention is to provide a stabilized lipid composition capable of providing the required quantity of LC-PUFA by an improved absorption without reducing the absorption of calcium, intended to be incorporated into a dietetic product without the latter undergoing oxidative or nutritional degradation because of this incorporation.
Thus, the stabilized lipid composition according to the invention consists of randomly interesterified TAGs comprising, by weight of fatty acid residues, less than 5% by weight of LC-PUFA as C20 and above, with a degree of unsaturation of 4 and above, comprising predominantly AA, DHA or EPA, and at least 80% by weight of MC-SFA as C6 to C14, where the TAGs containing LC-PUFAs consist practically exclusively of mono-LC-PUFA.
MC-SFA as C6 to C14 designates the medium-chain saturated fatty acids which are rapidly absorbed by the body, which do not form insoluble soaps with calcium as is the case with the LC-SFAs and which do not negatively influence the absorption of calcium. Lipids that contain these fatty acids are chosen from the natural or synthetic MC-TAGs containing caproic, caprylic, capric, lauric and myristic acids. Coconut, babassu and palm kernel fats also may be mentioned.
The process for preparing the stabilized lipid compositions of the invention preferably comprises the following steps:
the chemical interesterification of a mixture containing i) 1 to 20% of an oil rich in LC-PUFA having a degree of unsaturation of 4 and above containing the acids AA, DHA or EPA and ii) 80 to 99% of an oil rich in MC-SFA, is carried out in the presence of sodium ethoxide or methoxide as catalyst, so as to randomly redistribute the fatty acids on the glycerol backbone,
the product of the reaction is washed with an aqueous medium so as to free it of the alkaline and soap residues,
the washed product is refined by bringing into contact with an adsorbent which retains the traces of soap and of secondary products of the reaction and separating the adsorbent, and
the refined product is deodorized by steam distillation at about 190xc2x0 C. under vacuum, which leads to a deodorized, decolorized and stabilized oil.
The reaction is carried out so as to minimize the quantity of water present in the starting oil mixture. Thus, it is preferably dried at 80-85xc2x0 C. under vacuum, for example of about 20 mbar, before the addition of the catalyst.
The catalyst should be fresh. Sodium methoxide or sodium ethoxide may be used, the latter being preferred. The quantity used is about 0.2% by weight, based on the starting mixture.
The starting oil mixture is heated up to the desired reaction temperature, preferably 80 to 90xc2x0 C. before adding the catalyst. This addition is carried out with vigorous stirring in order to disperse the catalyst homogeneously. The reaction is preferably carried out under a vacuum of about 20 mbar, for about 30 min.
After the reaction, water is added to the reaction mixture in order to inactivate the catalyst and to wash the soap residues formed. A salt such as NaCl may be added to the aqueous medium, for example at a concentration of about 2% by weight, in order to avoid the formation of an emulsion which would result in loss of oil. This washing step may be repeated once or twice in order to reduce the concentration of soap below about 200 ppm.
To remove the traces of soap, the washed oil is treated with an absorbent, for example a silica gel, and the oil is decolorized with a bleaching earth, these operations being preferably carried out by bringing the oil into contact sequentially with the absorbent and separating the refined oil from the absorbents, for example by filtration.
The refined oil is then deodorized by steam distillation at about 190xc2x0 C. for about 3 h under a high vacuum, for example of about 1 to 3 mbar. When desired, natural tocopherol may then be added as antioxidant.
The invention also relates to a nutritional product containing a lipid composition as defined above. It relates in particular to an infant food containing proteins, hydrolysed where appropriate, carbohydrates, lipids and where appropriate vitamins and trace elements, characterized in that it contains, by weight of dry matter, 15 to 35% of lipids of which 5 to 50% consist of the above lipid composition.
Nutritional product is understood to mean both a product for infant or adult clinical, for example enteral, nutrition and an infant food. Such a food may be prepared in liquid or powdered form with incorporation of the above lipid composition, by the wet mixing of the various constituents, followed by sterilization or pasteurization and aseptic packaging in the case of a liquid product or by drying, for example, spray-drying, or alternatively by dry mixing in the case of a powder.